1. Field of the Invention
The invention relates to a heating system for heating air, especially for heating the interior of a motor vehicle, with at least a first heater, at least a second heater, and at least one flow path between the first heater and the second heater. The invention also relates to a process for influencing air flows in a heating system for heating air, especially for heating the interior of a motor vehicle, with at least one first heater, at least one second heater, and at least one flow path between the first heater and the second heater. Furthermore, the invention relates to an air heater with a burner, a heat exchanger, an air inlet area, an air exit area, a control device and a temperature sensor which is located in the air inlet area, the temperature in the air inlet area being monitored by means of the temperature sensor which is located in the air inlet area. The invention likewise relates to a process for detecting hot air flowing back through an air heater.
2. Description of Related Art
The use of generic heating systems and generic processes known, especially in the motor vehicle art. Such heaters are characterized by the interaction of a first heaterxe2x80x94the motor vehicle heater or a combination of the motor vehicle heater and air conditionerxe2x80x94and a second heater, the auxiliary air heater. The motor vehicle heater or the combination of the motor vehicle heater and air conditioner is called the xe2x80x9cfront box.xe2x80x9d The combination of motor vehicle heater and air conditioner is also known as HVAC (Heat, Ventilation. and Air Conditioning). When in the description of the prior art and in the description of the invention a motor vehicle heater is addressed below, combinations of a motor vehicle heater with an air conditioner are also always intended.
FIG. 14 schematically shows the structure of a system of the prior art. A motor vehicle heater 110 with an air inlet 138 (which is not shown in detail) is connected to a mixing chamber 114. Furthermore, there is an auxiliary heater 112 which has an air inlet 136. The auxiliary heater 112 is also connected to the mixing chamber 114. The mixing chamber 114 has several air channels 140 for the emergence of air. Generally, in the mixing chamber 114, it is possible to reroute the volumetric flow entering there via flaps into the different air channels 140 or to close the air channels 140. In this way, the user is able to undertake various settings for climate control of the interior of the motor vehicle.
In normal operation of the heating system shown in FIG. 14, an air flow 142 emerges from the motor vehicle heater 110 and enters the mixing chamber 114. Likewise, an air flow 144 emerges from the auxiliary heater 112 and enters the mixing chamber 114. As a result of these air flows 142, 144, which are inherently independent of one another, countercoupling can result which can lead, for example, to a counterpressure 146 against the flow 144 of the auxiliary heater 112. In FIG. 14, the counterpressure 146 is a small amount so that proper operation of the heating system is possible.
FIG. 15 shows a system with a structure which corresponds to that from FIG. 14. In contrast to the operating state which is shown schematically in FIG. 14, the heating system as shown in FIG. 15 does not work properly. This results from the increased counterpressure 146 which, in this case, is so great that it causes a reversal of the air flow 144.
The formation of the operating states shown in FIG. 14 and in FIG. 15 and the resulting problems are explained below.
The motor vehicle heater has a fan which blows air into the mixing chamber with a high volumetric flow and relatively low pressure stiffness. The term pressure stiffness is defined as the potential of a pressure build-up. A high pressure stiffness stands, for example, for the potential to apply a high pressure. The fan of the motor vehicle heater can be controlled continuously or in stages, and this control can be undertaken especially independently of the thermodynamic states in the heating system.
In addition, the auxiliary heater has a fan. The latter, in contrast to the fan of the motor vehicle heater, is relatively pressure-stiff, but with a smaller volumetric flow being produced. In current auxiliary heaters, the fan of the auxiliary heater, in principle, cannot be controlled independently of the heat output of the auxiliary heater. When more heat output is required, the volumetric flow is also increases and vice versa. Based on the change of the volumetric flow of the auxiliary heater, however, the pressure stiffness also changes. The blow-out temperature on the auxiliary heater is dependent, among others, on the resistances opposing the auxiliary heater. For a high resistance, this can lead to an elevated blow-out temperature which is limited by adjusting the auxiliary heater down or turning it off.
Therefore, for operation of the auxiliary heater, it is ideal if it can run at low outside temperatures, with high heat outputs, i.e., high volumetric flows, and thus, high pressure stiffness. The auxiliary heater can then react to the fan of the motor vehicle heater, especially when the latter is operated at low fan stages or if only a few flaps in the mixing chamber are closed.
The problem arises when the auxiliary heater must reduce the heat output as a result of rising temperatures. Based on the above described regularities, then the pressure stiffness, and moreover, the possibility of adequately reacting to the motor vehicle fan decrease, a state results in which the resistance for the auxiliary heater becomes higher and higher, and the auxiliary heater continually adjusts the heat output down. This can lead to the counterpressure which is produced by the motor vehicle heater fan being higher than the pressure of the auxiliary heater. This state is also called overpressurization. The heat of the auxiliary heater can then no longer be delivered. In the extreme case, it is transported in the opposite direction. This can lead to the fact that the overheating protection generally located in the outlet area of the auxiliary heater can be shut down. Furthermore, serious damage to the entire system can occur, for example, in the inlet area or on the control device of the auxiliary heater.
Therefore, a primary object of the present invention is to provide a heating system and a process which eliminate the aforementioned disadvantages and which especially prevent overpressurization in the heating system.
This object is achieved with the features of the invention described below.
The invention is based on a generic heating system in that there is at least one auxiliary fan with which a flow can be produced in the direction from the second heater to the first heater. This makes it possible to increase the volumetric flow or the pressure from the second heater in the direction of the motor vehicle heater to such an extent that the second heater is not overpressurized under any conditions. Furthermore, there is no need to dam the flow connection between the second heater and the motor vehicle heater, stable and careful heater operation being ensured nevertheless. In this way, even at low rpm of the second heater, overpressurization can be prevented. In the second heater, on the average, lower temperatures prevail so that the components are less stressed. Uniform operation of the second heater, which requires especially fewer control cycles, can take place by which the burner in the second heater is less stressed. Furthermore, the heat energy contribution of the second heater can be increased since the maximum heat output becomes greater. A cleaner start and burnout cycle can be ensured. Since it is not necessary to interrupt the flow connection between the first heater and the second heater, the heat energy from the second heater is always optimally used.
The invention develops its advantages especially in that the first heater is the motor vehicle heater and that the second heater is the auxiliary heater. The invention can be used advantageously for the interplay of heaters in any environment. Special advantages arise however when used in a motor vehicle. There, auxiliary heaters are often combined with motor vehicle heaters or with motor vehicle heating systems which are already in use. The invention enables easy integration by making available stable flow conditions of the auxiliary heater which is to be incorporated in the vehicle system.
Preferably, there is at least one mixing chamber which air can enter which has flowed out of at least the first heater and out of at least the second heater. Such a mixing chamber can be used to route air with a uniform temperature into the interior of the motor vehicle. The connection of the motor vehicle heater to the auxiliary heater generally takes place via this mixing chamber, and then problems in overpressurization can also occur. In particular, a mixing chamber often has flaps with which channels can be entirely or partially closed so that the counterpressure against the flow from the auxiliary heater can be very high.
It is especially advantageous that the auxiliary fan is located upstream of the second heater. This position is preferable since, in this way, the auxiliary fan is not exposed to thermal stress. Likewise, it is possible for the auxiliary fan to be moved into the area of the air inlet of the auxiliary heater. However, it is also within the scope of this invention to place an auxiliary fan behind the auxiliary heater. This is possible especially when an auxiliary fan is chosen which withstands higher thermal stress.
In another, especially preferred embodiment, the heating system in accordance with the invention is developed such that the auxiliary fan can be actuated depending on the output signal of a control device. Such a control device can incorporate numerous input data in the decision whether to actuate the auxiliary fan. Here, input signals are considered which are linked directly to the heating system. However, also other signals can be evaluated, for example, CAN bus signals.
It is especially advantageous that, to detect the pressure states in the heating system, there is at least one pressure sensor for generating an input signal for the control device. Such a pressure signal can be produced, for example, by a pressure differential sensor, the difference between the pressure upstream of the auxiliary heater and the pressure in or downstream of the auxiliary heater being measured. When the pressure difference is too high, there is a high probability of overpressurization, so that measures can be initiated by the control device, for example, the auxiliary fan can be connected. It is also possible for damming to occur at low pressures. Likewise, for example, at high rpm, there can be a high pressure without damming.
In the same sense, it is preferred that, to detect the pressure states in the heating system, there is at least one pressure sensor for generating an input signal for the control device, temperature signals can be evaluated, for example, by gradient evaluation. If the temperature sensor is installed, for example, in the vicinity of the output of the auxiliary heater, in the case of overpressurization, a sudden temperature drop can occur in the area of this temperature sensor. Since such a temperature drop could not be present at a uniform or increasing heat output without the presence of overpressurization, overpressurization can be concluded from the temperature drop. Likewise, it is possible to install several temperature sensors in the area of the auxiliary heater and to draw conclusions regarding a possible overpressurization from the three-dimensional temperature variation.
It is especially preferred that the auxiliary fan can be controlled. This control can take place continuously or in steps, these control tasks preferably being assumed by the control device of the auxiliary heater. It is likewise possible to provide control which takes place in increments or which is continuous. In another operating mode, the system can be designed such that the auxiliary fan is only turned on or off. To do this, for example, a relay can be used.
It can likewise be advantageous for the auxiliary fan to be actuated directly depending on the output signal of the temperature sensor. Such a temperature sensor can be, for example, a bimetallic component so that triggering of the auxiliary fan can take place independently of the control device.
The invention is based on the generic process in that at least one auxiliary fan produces a flow in the direction from the second heater to the first heater. In this way, the properties explained in conjunction with the heating system and the advantages of the invention are also implemented within the framework of the process. This likewise applies to the embodiments of the process indicated below.
The invention develops its advantages especially in that the first heater is the motor vehicle heater and that the second heater is the auxiliary heater.
Preferably, there is at least one mixing chamber which air can enter which has flowed out of at least the first heater and out of at least the second heater.
It is especially advantageous that the auxiliary fan is actuated depending on the output signal of the control device.
In the aforementioned connection, it is especially advantageous that pressure states in the heating system are detected by at least one pressure sensor and that a pressure-dependent input signal for a control device is produced.
In the same sense, it is preferred that temperature states in the heating system are detected by at least one pressure sensor and that a pressure-dependent input signal for a control device is produced.
Furthermore it can useful for the auxiliary fan to be controlled.
In another useful embodiment of the process of the invention, it is provided that the auxiliary fan is actuated directly depending on the output signal of the temperature sensor.
It can be useful for the auxiliary fan to be turned on and off when the second heater is turned on and off. The auxiliary fan is therefore used only for support for the fan of the second heater and especially only during heating operation of the second heater.
However, it can also be useful for the auxiliary fan to be turned on and off when the first heater is turned on and off. Since there is the danger of overpressurization of the heating system during the turn-on phase of the first heating system, such an operating mode of the auxiliary fan can be efficient.
In another version, the auxiliary fan is turned on when overpressurization of the heating system is detected. In this way, the operating time of the auxiliary fan is minimized since it is only turned on when the state for which the heating system with an auxiliary fan is designed is present.
The invention is based on a generic air heater in that when a boundary value is exceeded by a temperature-dependent quantity, the burner is transferred into a state with lower heat output. In this way, the temperature sensor which is used in normal operation to determine the air inlet temperature is used in the air inlet area of the air heater to determine the backflow of heated air. This takes place via determination of a temperature-dependent quantity. If this temperature-dependent quantity exceeds a certain boundary value, countermeasures can be taken in which especially the burner is transferred into the state with lower heat output. Consequently, undesirable overheating of electronic components, for example, in the area of the control device, is opposed.
For example, the air heater of the invention can be used such that, when the boundary value is exceeded by the temperature-dependent quantity, the burner is turned off. Consequently, further heating of hot air is minimized, by which an especially effective countermeasure is made available.
Furthermore, within the framework of this invention, it can be provided that the temperature-dependent quantity is the temperature gradient over time so that when the maximum positive temperature gradient is exceeded, the burner is turned off. The rate of temperature increase can therefore be used as the criterion since a more or less sudden temperature rise indicates incipient flow reversal. Therefore, by monitoring the temperature gradient, a countermeasure against flow reversal or against overheating of the components in the entry area can be taken.
Likewise, alternatively or in addition to the gradient evaluation, it is possible for the temperature-dependent quantity to be the temperature itself so that when the maximum temperature is exceeded, the burner is turned off. For example, if the temperature in the area of the temperature sensor in the air inlet area increases only slowly, this yields additional safety.
It is likewise possible for aftercooling to be carried out with or after transfer of the burner into a state with lower heat output. This aftercooling results in that components which may already be in the critical temperature state can be re-cooled quickly so that afterwards it is possible to pass back into normal burner operation.
Moreover, the invention includes a process for detecting backflowing hot air through an air heater in which the temperature in the air inlet area is monitored by a temperature sensor which is located in the air inlet area and when a boundary value is exceeded by the temperature-dependent quantity the burner of the air heater is transferred into the state with lower heat output. In this way, the advantages described in conjunction with the air heater of the invention are also realized within the framework of a process. This also applies to the advantageous embodiments of the process of the invention indicated below for detecting the back-flowing hot air.
The process in accordance with the invention is especially advantageous when the burner is turned off when the boundary value is exceeded by a temperature-dependent quantity.
It is likewise especially useful if the temperature gradient over time is used as the temperature-dependent quantity so that when a maximum positive temperature gradient is exceeded the burner is turned off or is transferred into the state with lower heat output.
Furthermore, the process according to the invention can be especially advantageously designed so that, in addition or alternatively to the gradient evaluation as the temperature-dependent quantity, the temperature itself is used so that when a maximum temperature is exceeded the burner is turned off.
Likewise, within the framework of the process of the invention, it can be useful to carry out aftercooling with or after the transfer of the burner into the state with low heat output.
The invention is based on the finding that overpressurization and the associated problems in the area of an auxiliary air heater can be overcome by providing an auxiliary fan. In this way, it can be ensured that the volumetric flow and the pressure stiffness in the direction from the second heater to the first heater are always sufficient to overcome the counterpressure which is produced by the motor vehicle heater. Flow reversal within the air heater can be detected, for example, using the evaluation of a temperature gradient over time.
The invention is explained by way of example with reference to the accompanying drawings using preferred embodiments.